1. Field of the Invention
The present invention relates to a keyboard apparatus of an electronic keyboard instrument, and more particularly, to the structure of a key-fulcrum function device of a keyboard apparatus and miniaturization of the keyboard apparatus.
2. Description of the Related Art
In electronic keyboard instruments such as portable keyboard, synthesizer, electronic organ, and electronic piano, a conventionally known keyboard apparatus includes a plurality of key units which are stacked together and fixed to a key frame and each of which is comprised of a plurality of keys (for instance, see FIGS. 2 and 3 of Japanese Patent Publication No. 2628566).
FIGS. 5A and 5B are schematic views for explaining a problem of a conventional key unit.
By way of example, the conventional key unit includes one-octave keys that are divided into a first structure (black key unit) having a plurality of black keys and a plurality of second structures (e.g., a white key unit comprised of four keys of C, E, G, and B and another white key unit comprised of three keys of D, F, and A), in each of which at least every two white keys are formed into a comb-teeth like shape. The keys of each key unit have rear ends thereof coupled together into a common base end and integrally formed by resin molding. The key units are stacked together at their common base ends and fixed to a key frame.
Referring to FIG. 5A, a plurality of key main bodies 51 to 53 forming a white key unit have rear ends thereof fixed to a band-like common base end 54 via horizontal hinges 51a to 53a which can be elastically deformed. The key main bodies 51 to 53 are capable of being pivoted around the horizontal hinges 51a to 53a in the key depression/release direction.
Reference numerals 55 to 57 denote guide portions (key guides) which are formed in the key frame, not shown, so as to project along back surfaces of the key main bodies 51 to 53. These key guides 55 to 57 limit displacements of the key main bodies 51 to 53 in the width direction (the left-to-right direction) of the keys and also limit the rolling of the key main bodies 51 to 53 around the longitudinal axes (extending in the depth direction) of the keys.
However, in the molding of the key unit, there is caused an error from the design dimension or a deformation of the key unit due to post shrinkage thereof or the like. If such an error or deformation is caused in the key main bodies 51 to 53 or the common base end 54, an undesired force is locally exerted when the key unit in which an error or deformation is caused is forcibly mounted to the key frame.
For instance, if the key main body 53 is deformed, the deformed key main body 53 causes the horizontal hinge 53a to be deformed in the width direction of the key, as shown in FIG. 5B, which in turn causes another key to be deformed via the common base end 54. As a result, the key guides 55 to 57 are in urged contact with the back surfaces of the key main bodies 51 to 53 at locations a, b, and c. This is also true in a case where illustrated portions d and e of the common base end 54 are deformed. As a consequence, bad effects are caused such that the key main bodies 51 to 53 are rubbed against the key guides 55 to 57 or the adjacent key main bodies are rubbed against from each other.
FIG. 6 is a view of a key for explaining another problem of the conventional key unit (see, FIGS. 1 and 4 of Japanese Patent Publication No. 2628566).
In FIG. 6, reference numeral 61 denotes a key main body, 61a denotes a horizontal hinge whose rear end can be elastically deformed to permit the key main body 61 to be pivotable, 61b denotes a left-to-right hinge capable of being elastically deformed to permit the key main body 61 to be displaceable in the width direction of the key, and 62 denotes a band-like common base end.
The horizontal hinge 61a is a horizontal thin piece member, which is thin in thickness as viewed in the vertical direction of the key and extends in the longitudinal direction of the key. The left-to-right hinge 61b is a vertical thin piece member, which is thin in thickness in the width direction of the key and extends in the longitudinal direction of the key.
The horizontal hinge 61a is connected to the left-to-right hinge 61b via a connecting portion 61c, and the left-to-right hinge 61b is connected to the common base end 62 via a connecting portion 61d. Each of the connecting portions 61c, 61d is formed into a plate piece member having a thickness as viewed in the longitudinal direction of the key and extending in the width direction of the key.
Reference numeral 61e denotes a stopper piece member that includes a stopper disposed on the key-frame side for restricting a pivotal range of the key main body 61. In the key unit disclosed in Japanese Patent Publication No. 2628566 (refer to FIG. 1 of the Publication), the stopper piece member 61e also functions as a key guide by being inserted into a slit formed in the frame.
When the key main body 61 is deformed in the width direction of the key due to post-molding shrinkage, the horizontal hinge 61b is slightly bent and the key main body 61 is pivoted in the width direction of the key so as to correct the position of the key main body. As a result, an inclination of the key in the width direction of the key is adjusted such that the key main body 61 is made perpendicular to the common base end 62.
However, the key main body 61 is connected at its rear end with the common base end 62 extending in the longitudinal direction, via a key-fulcrum function device having a horizontal hinge 61a extending in the longitudinal direction. Thus, the keyboard apparatus is long in the depth direction. For this reason, an electronic keyboard instrument accommodating the keyboard apparatus is also long in the depth direction.
A space for mounting a switch and the like is required below the common base end 62 whose upper part is covered by an instrument body panel. For this reason, the instrument body panel must be disposed sufficiently above the common base end 62, which causes a problem.
Another type of keyboard apparatus has been known in which a vertical hinge is used as a key-fulcrum function device (refer to Japanese Utility Model Registration Publication No. 6-31507).
Keys forming a key unit have intermediate portions thereof (at which a rear surface of a black key is present) as viewed in the longitudinal direction. At the intermediate portion of each of the keys, there is formed a vertical hinge comprised of a thin plate piece member, which is thin in the longitudinal direction of the key and which extends downward of the key. The vertical hinge functions to permit a distal end of the key to be pivotable in the key depression/release direction. The vertical hinge is coupled to and integrally molded with a band-like common base end, which is placed on the same plane as the vertical hinge. In the keyboard apparatus disclosed in Japanese Utility Model Registration Publication No. 6-31507, the keys each have a rear portion thereof provided with a weight or formed into a shape in contact with a lever to which a weight is fixed. Therefore, the key main bodies are extended rearward beyond positions at which rear surfaces of black keys are located.
If the rear ends of the keys are not extended rearward but are extended downward to form vertical hinges, the keyboard apparatus can be shortened in the longitudinal direction of the keys as compared to using horizontal hinges.
At that time, if the vertical hinges are extended downward sufficiently in length, the vertical hinges are capable of being deformed while being twisted when applied with a force exerting in the width direction of the keys, making it possible to broaden a movable range thereof. However, in that case, since the vertical hinges move while being obliquely twisted, a stress is concentrated at root portions of the vertical hinges, thus the durability of the vertical hinges is deteriorated. In addition, rolling motions of the vertical hinges are liable to occur, producing mechanical noise due to the contact of the vertical hinges with adjacent key main bodies or key guides, which causes a problem.